114 PROCEEDINGS OP THE ACADEMY OP 



thirty miles above its mouth, then forms a high dividing ridge between the 

 Moreau and Shyenne rivers, at -which locality it first took its name. Con- 

 tinuing thence its south westerly course, it crosses the Shyenne, and is seen 

 again in its full thickness at the heads of Opening creek and Teton river, form- 

 ing a high ridge from which tributaries of the Shyenne and Teton take their 

 rise. The little streams flowing into the Shyenne have a north westerly course, 

 while those emptying into the Teton take a south easterly direction. We thus 

 find that this bed underlies an area of about two hundred miles in length and 

 fifty miles in breadth, or about ten thousand square miles. 



The general character of Formation No. 5 is a yellow arenaceous and 

 argillaceous grit, containing much ferruginous matter, and in localities a 

 profusion of Molluscous fossils. It forms a much more fertile soil, more 

 healthy and luxuriant vegetation, sustains a finer growth of timber than 

 Formation No. 4, and abounds in springs of good water. 



Like No. 4, this bed yields in the greatest abundance quite perfect and well 

 preserved organic remains. Many of the species approximate so closely to 

 Tertiary forms, that did we not find them everywhere associated with Am- 

 monites, Scaphites and other genera which are not known to have existed later 

 than the Cretaceous epoch, we should at once pronounce the formation in 

 which they occur Tertiary. The whole thickness of this bed is estimated at 

 one hundred to one hundred and fifty feet. 



System III. — Tertiary. 



This system occupies an extensive area in the country bordering on the 

 Missouri valley. Its wide geographical distribution, its influence upon the 

 topographical features of the country, the mixed and somewhat peculiar cha- 

 racter of its organic remains, render its study of the highest interest to the geolo- 

 gist and palasontologist. It seems to occupy depressions in the Cretaceous strata, 

 as is shown in the illustrative section. I shall speak of this sj'stem on the 

 Upper Missouri as they occur, or as three distinct basins, the intervening por- 

 tions being occupied by rocks, which, as far as has been determined, belong 

 to the Cretaceous epoch. 



The Basins of this systems are as follows : — 



1st. — Les Mauvaises Terres, or Bad Lands of White river, which with their 

 outliers occupy an area of from two hundred to two hundred and fifty miles 

 in length and one hundred to one hundred and fifty in bi-eadth. Exact limits 

 not yet ascertained. 



2nd. — The Great Lignite Basin, commencing near the mouth of Cannon 

 Ball river and extending nearly to the mouth of the Muscle Shell river, a 

 distance of about six hundred miles. I have traced this formation up the 

 Yellow Stone to the mouth of the Big Horn river, a distance of three hundred 

 miles. Its limits have not been ascertained in several directions. 



Zrd. — The Bad Lands of the Judith river, which occupy an area of forty miles 

 in length and fifteen to thirty in breadth, reposing upon a sandstone, the age of 

 which has not been positively determined. 



Basin \st. — Bad Lands of White River. 

 This most remarkable lacustrine deposit has been comparatively but recently 

 made known to the scientific world. Wondierfnl not alone for its unique scenery, 

 but also for the abundance and importance of its organic remains. Even as yet it 

 has been but partially explored, and yet the results that have been obtained 

 have proved of the highest interest. The profusion of Mammalian and Chclo- 

 niau remains contained in this deposit of species and in most cases genera, 

 though closely allied yet differ from all known living forms, which must render 

 it, when fully explored and studied, classic ground to the geologist and pal;^- 

 ontologist. A history of the progress of its exploration up to 1853, with 

 elaborate descriptions of many of its organic remains, may be found in a 

 magnificent memoir entitled " The Ancient Fauna of Nebraska," written by 

 t'rof. Joseph Leidy, and published by the Smithsonian Institution. 



[May, 



